The bandwidth shortage increasingly experienced by mobile carriers has motivated the exploration of the underutilized Millimeter Wave (mmWave) frequency spectrum between 3G and 300G Hz for the next generation broadband cellular communication networks. The available spectrum of mmWave band is two hundred times greater than the conventional cellular system. The mmWave wireless network uses directional communications with narrow beams and can support multi-gigabit data rate. The underutilized bandwidth of the mmWave spectrum has wavelengths ranging from 1 mm to 100 mm. The very small wavelengths of the mmWave spectrum enable large number of miniaturized antennas to be placed in a small area. Such miniaturized antenna system can produce high beamforming gains through electrically steerable arrays generating directional transmissions.
With recent advances in mmWave semiconductor circuitry, mmWave wireless system has become a promising solution for real implementation. However, the heavy reliance on directional transmissions and the vulnerability of the propagation environment present particular challenges for the mmWave network. In general, a cellular network system is designed to achieve the following goals: 1) Serve many users with widely dynamical operation conditions simultaneously; 2) Robust to the dynamics in channel variation, traffic loading and different QoS requirement; and 3) Efficient utilization of resources such as bandwidth and power. Beamforming adds to the difficulty in achieving these goals.
Maintaining antenna pointing and tracking accuracy is essential in many phases of the communication process. In principle, beam administration/training mechanism, which includes both initial beam alignment and subsequent beam tracking, ensures that base station (BS) beam and user equipment (UE) beam are aligned for data communication. Hierarchical level beam pattern is assumed in wireless or cellular networks. Different beamformers can have different spatial resolution. For example, a sector antenna can have shorter by wider spatial coverage, while a beamforming antenna can have longer by narrower spatial coverage. To provide moderate array gain, large number of array elements may be needed.
There are two types of beamforming: switched beamforming and adaptive beamforming. Adaptive beamforming means digital beamforming. The complexity of adaptive beamforming is high with flexible beam patterns, while beam alignment time is acceptable. Switched beamforming is analog or hybrid beamforming. The complexity of switched beam forming is low, while beam patterns are not flexible and beam alignment time is long. Beam administration methods are sought to perform beam alignment and beam tracking for both BS and UE.